Problem: $ { \left[\begin{array}{rr}{-1} & {-1} \\ {0} & {0} \\ {0} & {1}\end{array}\right]+\left[\begin{array}{rr}{0} & {-2} \\ {-1} & {-1} \\ {-2} & {0}\end{array}\right] = {?} } $
Answer: To find the sum of two matrices, add the corresponding items between each matrix. ${\left[\begin{array}{rr}{-1}+{0} & {-1}+{-2} \\ {0}+{-1} & {0}+{-1} \\ {0}+{-2} & {1}+{0}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rr}{-1} & {-3} \\ {-1} & {-1} \\ {-2} & {1}\end{array}\right]}$